PROJECT SUMMARY Prostate cancer is the most commonly diagnosed cancer among men in the United States (US), with more than 220,800 new diagnoses expected in 2015. While a large proportion of new cases appear to have clinically indolent tumors, prostate cancer remains the second-leading cause of cancer death among men in the US. Preventing progression of initially localized prostate cancers to lethal disease is a key priority. Evidence from our group and others suggests that lifestyle factors after prostate cancer diagnosis may prevent non-metastatic prostate cancer from becoming lethal disease. We recently developed an 11-factor score based on lifestyle practices after diagnosis that is strongly associated with reduced risk of prostate cancer death (unpublished). Men with 4-7 and 8-11 points (vs. 0-3) had a 48% (HR= 0.52, 95%CI=0.32, 0.84) and 75% (HR=0.25; 95% CI=0.09, 0.69) lower risk of prostate cancer death, respectively. Based on these compelling data, we developed a lifestyle program delivered via the Internet for prostate cancer patients, with the ultimate goal of improving clinical outcomes in men with prostate cancer by incorporating a lifestyle intervention as adjuvant therapy to standard prostate cancer management. In this proposal, we aim to address the critical question ? does access to an Internet-based lifestyle program (designed to increase exercise +/- improve diet quality) impact prostate biology and reduce risk of prostate cancer progression? We propose to conduct a 2-year 3-arm (web-based intervention targeting exercise vs. web-based intervention targeting exercise + diet vs. usual care) randomized controlled trial among 150 prostate cancer patients opting for surgery at the University of California, San Francisco. Men will be enrolled eight weeks before radical prostatectomy and complete follow-up assessments 6 months, 1 year, and 2 years post-surgery. Men assigned to the intervention arms will receive a two-year web- based lifestyle program post-surgery and text messaging tailored to the intervention (i.e., exercise or exercise + diet) and Fitbits. We will examine the effect of exercise vs. exercise + diet vs. usual care on: 1) a validated, FDA- approved prognostic score, Decipher, measured in biopsy (pre-intervention) and prostatectomy (post-initial 8- week intervention period) tissue; 2) mRNA expression of cancer-related pathways in tumor and normal tissue from biopsy and prostatectomy; 3) detectable PSA post-surgery and risk of prostate cancer recurrence at 2- years after radical prostatectomy; and 4) sexual and urinary function at 6 months, 1 year, and 2 years post- surgery. This study will provide critical translational data on the effect of a sustainable Internet-based intervention on prostate tumor biology and clinical outcomes in men with prostate cancer. These data will support the use of lifestyle interventions as adjuvant therapy for prostate cancer. Strengths of this proposal include our novel, evidence-based, intervention; highly relevant preliminary data; innovative prognostic biomarker outcome; and experienced multi-disciplinary team with outstanding track record.